The present invention generally relates to a track sensor for tracking an optical link between satellites. More particularly, the present invention relates to a track sensor including a multi-channel photodetector for use in tracking an optical link between terminals based on the received power per channel from a communication optical beam.
One of the difficulties in long distance optical communication (such as laser communication) is maintaining an established optical communication link between transmitting and receiving communication terminals. The optical communication link may be negatively affected by such factors as the relative positional changes of the terminals, jitter in the terminals, or pointing error. The receiving and transmitting terminals may be either satellite or ground stations.
To maintain communication, the pointing of the optical beams must be adjusted to reflect the movement of the receiving terminal with respect to the transmitting terminal. This may be done by employing an optical sensor to detect changes in the optical beam pointing and then compensate for these changes by, for example, re-orienting the beam steering using mechanism driven optical elements
Prior art systems employed devices such as additional optical beacons directed to specific track sensors on the receiving satellite to maintain correct communication beam pointing. Multiple optical beacons increase cost in terms of both the size and weight of the satellite and the power consumption of the beacon. Other systems relied on hyper-accurate positioning, which may not be achievable when the separation between terminals is large and may be easily disrupted by spacecraft jitters.
Thus, a need has long existed for a tracking system and sensor that minimizes power consumption and additional weight and size while providing reliable, fault tolerant, and quickly achievable tracking of an optical communications beam.
One object of the present invention is provide an optical tracking sensor for use in an optical tracking system that eliminates additional laser beacon signals.
Another objective of the present invention is to minimize the cost, complexity, size, weight, and power consumption of the hardware used to provide the tracking system and sensor.
One or more of the foregoing objects are met in whole or in part by the inter-satellite optical link track sensor of the present invention. The present invention provides a tracking sensor and system to maintain the alignment of an optical communication beam between two terminals so that the two terminals may communicate.
The tracking sensor includes a multi-channel photodetector and channel circuitry including a synchronous demodulator and at least one adder. A received optical signal is converted to an electrical signal by the photodetector and supplied to channel circuitry. The channel circuitry determines the power of the received signal by synchronously demodulating the received signal. A signal representing the power of at least two channels is supplied to the at least one adder to sum the received power. The determination of the power received per channel allows the receiving terminal to calculate its pointing error.
These and other features of the present invention are discussed or apparent in the following detailed description of the preferred embodiments of the invention.